Compact ECR ion sources have been developed for high energy carbon-ion radiotherapy (C-ion RT). Three compact ECR ion sources have been developed as the prototype at NIRS. The first ion source was used the microwave of 2.45 GHz to reduce the construction cost of the source as much as possible. This ion source could not obtain enough intensity of C2+ because there were problems in microwave injection and beam extraction system. The second and third ion sources, named Kei and Kei2, solved these problems. The structure of Kei and Kei2 were similar, however Kei2 improved on the magnetic field configuration. The beam intensity of 0.26 mA and 0.78 mA for C4+ were obtained by Kei and by Kei2, respectively. All of later C-ion RT facilities in Japan, the Gunma University Heavy Ion Medical Center, the Saga Heavy Ion Medical Accelerator in Tosu, and the Ion-beam Radiation Oncology Center in Kanagawa, installed copies of Kei2 and named them KeiGM, KeiSA, and KeiGM3. On the other hand, the original Kei2 have been installed in the HIMAC at NIRS and produces carbon beams for experimental use. Developments and some improvements of these Kei-series ECR ion sources will be reported.